The Study of Ebv Encoded Bart Micrornas and Their Roles in Npc Pathogenesis

Background: Nasopharyngeal carcinoma (NPC) is a human malignancy in which cancer cells arise from the epithelial cells of the nasopharynx tissue. Compelling evidence indicate that EBV is a causal agent of NPC and suggest that products of EBV genome are involved in the development of the malignancy. In addition to viral proteins, EBV also encodes several non-coding RNAs, including EBV-specific microRNAs. Despite their presence in NPC cells, the roles of these EBV microRNAs in NPC pathogenesis have not been well explored. Recently, we utilized the next generation sequencing technology to characterize the EBV microRNA transcriptome in NPC tissues. We discovered that three EBV-encoded microRNAs, BART3, BART5 and BART9, were expressed at high levels in all NPC tissues examined. The abundance of these EBV microRNAs were higher than the best documented human oncogenic microRNA, miR-21. Among these three microRNAs, BART5 has been shown to promote host cell survival by targeting a pro-apoptotic molecule, p53-upregulated modulator of apoptosis (PUMA). Our in-house target prediction and pathway enrichment analysis revealed that these three EBV microRNAs may each target a distinct set of cellular genes and regulate different pathways related to host cell proliferation, migration and immune responses, suggesting that all three EBV microRNAs may contribute to the NPC pathogenesis. Moreover, two critical tumor-suppressive pathways, p53-signaling and apoptosis, are significantly co-targeted by these three EBV microRNAs, suggesting that these EBV microRNAs may function in concert to contribute to multi-step formation of NPC. Interestingly, all these three highly abundant EBV microRNAs share their seed sequence with human microRNAs. As seed sequence is critical in determining microRNA target spectrum, it is likely that these EBV microRNAs may also regulate cellular functions by mimicking or antagonizing the biological activity of critical host microRNAs. Aim and strategy: In this proposal, we aim to elucidate the roles of these three EBV miRNAs in NPC tumorigenesis, either working alone or in combination. This project pursues three goals: first, we will explore the pathological roles of these EBV microRNAs in NPC formation. Specifically, we will use in vitro assays to examine the functional effects of individual microRNAs. We will use the in vivo animal model to investigate the potential cooperativity of these EBV miRNAs in NPC tumorigenesis. Second, we will investigate the underlying mechanisms regulated by these EBV microRNAs. Toward this end, genome-wide transcriptomics analysis, pathway enrichment analysis and microRNA target prediction will be used to elucidate the molecular targets and pathways regulated by these EBV microRNAs. Clinical relevance of these microRNA-regulated targets and pathways in NPC will also be assessed. Finally, we will investigate the potential interaction between EBV microRNAs and human oncogenic and/or tumor suppressive miRNAs. Specifically, we will examine the effect of BART9 on the expression levels and functions of miR-200 family. Similarly, the effect of BART5 on the expression and function of miR-18a/b will be investigated. Significance and future application: The ultimate goal of this study is to explore the potential of targeting EBV-encoded microRNAs for NPC diagnosis, prognosis and therapeutics. The proposed studies could advance our understanding of the biological functions and pathways regulated by these highly abundant EBV microRNAs and provide useful strategies to control the progression of NPC. In addition, the knowledge gained from this study will help to understand the cooperativity among viral microRNAs and the interaction between virus- and host-encoded microRNAs. This information can potentially be extended to other virus-encoded microRNAs and can be used in both basic and translational research.

Project ID:PC10008-0511
External Project ID:NSC100-2320-B182-023